2,3,7,8-Tetrachlorodibenzo-p-dioxins (TCDD) is the prototype of a number of chlorinated dibenzo-p-dioxins, dibenzofurans, azoxybenzenes, and biphenyls which are: 1) all approximate isostereomers, 2) all produce a similar toxic syndrome and 3) all bind to a specific cytosolic protein and initiate the induction of aryl hydrocarbon hydroxylase activity (AAH). We propose to a) study the molecular mechanism of toxicity of TCDD and search for an isolated cell system in which to examine its toxicity, b) continue to examine the mechanism of AHH induction mediated by the TCDD-receptor complex.